Process for the magnetic separation of ores



C. THOM, R. W. DIAMOND AND S. G. BLAYLOCK.-

PROCESS FOR THE MAGNETIC SEPARATION OF ORES.

APPLICATION FILED APR 30, 1920. RENEWED ocT. 14.1921.

1,398,05 l Patented Nov. 22, 1921.

How Sfieef f5) Maynefz'c Separalz'on of Orcs.

Bali 717f E/ccfr'o Mclq nefz'c MIC/1 in @5- UNITED STATES PATENT OFFICE.

CLARENCE mom, RALPH WILLIAM DIAMOND, AND SELWYN GWILL'YM BLAYLoox,

or TRAIL, BRITISH COLUMBIA, CANADA, ASSIGNORS 'ro THE CONSOLIDATED MIN- ING a smELrmG COMPANY 01 CANADA, LIMITED, or MONTREAL, QUEBEC,

CANADA.

Specification of Letters'l'atent.

Patented Nov. 22, 1921.

Application filed April 80, 1920, Serial No. 377,929. Renewed October 14, 1921. Serial No. 507,774.

T 0 all whom it may concern:

Be it known that we, CLARENCE THOM, a citizen of the United States, and RALPH WILLIAM DIAMOND and SELWYN GWILLYM BLAYLOCK, British sub'ects, residents of the city of Trail, in the istrict of Kootenay and Province of British Columbia, Dominion of Canada, have invented a new and useful Process for the Magnetic Separation of Ores; and we hereby declare the following to be a full, clear, and exact description of the same.

Our invention relates to a process by which some sulfid ores may be made highly susceptible to magnetic influence for the magnetic separation of the constituents, and involves four consecutive steps, two of which are interdependent and of the utmost importance to the success of the final operation.

The first step, is to heat the ore, without roasting, to a temperature, which when the ore is properly cooled, will yield the maximum magnetic susceptibility.

The advantage 0 this is, that when a sulfid ore, for example one containing free and combined iron compounds such as pyrrhotite and marmatite respectively direct from the mine, is ground fine and subjected to magnetic separation, only about 25% of the total iron content is sufiiciently amenable to magnetic influence to be separated by commercial magnetic machines. \Vhen the ore is subjected to a heat of from 800 F. to 1200 F. according to its fineness and the ore is allowed to cool slowly practically 100% of the pyrrhotite is rendered sufiiciently susceptible to be separated by the same magnetic machines. The best results are obtained when the ore is heated in a coarse state-two inch pieces being easiest to handle, but pieces as large as 6 inches cubed may be heated and the cores of the pieces as well as the outer rims will be rendered magnetic without the interior becoming oxidized. An over heat of the ore, however, is detrimental to the process, and therefore it is necessary to stay within temperature limits as well as time limits, these limits being governed by the ore being treated, as ores from different mines and localities may require difierent temperature and time treatments. For some ores it is found that a temperature of about 1200 R, if the ore is allowed only a few minutes exposure to the heat-enough to barely heat the larger pieces through-will give good results. this high heat for too long a time and any oxidatlon or even a tendency to melt the sulfid out of the ore occurs, the resulting separation of the pyrrhotite from the other minerals is poor. f too, a period of heating even at 1000 F. is continued too long, the same poor result is obtained.

Satisfactory results are obtained by exposlng the ore which has been crushed ,to about two inch mesh to a heat of 1000" F. for about nine minutes.

The progress of the ore through the kiln being relatively rapid, it is possible for the exteriors of the lumps to attain approximately a dull red heat without the interiors of the lumps becoming heated, during the direct action of the heat treatment in the kiln, and as this thorough heating of the lumps is essential for the success of the process, sufficient time must elapse during the cooling for the heat to travel through the lump by conduction.

The second step in the process, therefore, is the slow cooling of the ore after heating. If the hot ore is suddenly cooled by immer sion, very poor results are obtained. In fact, in general the magnetic susceptibility of the ore is then nearly as low by this treatment as for green ore without heating. If, however, a period of fifteen minutes is allowed to elapse before the ore is cooled to a temperature of about 400 F., there is only a slight loss in the magnetic suscep tibility.

The third step in the process is wet grinding in a ball mill or by any common grinding practice.

The fourth step is the magnetic separation of the magnetic sulfids from the gan e and other minerals, this being accomplis ed by passing water ore pulp over commercial magnetic machines.

To explain how the process may be .conveniently operated, we have shown in the diagrammatic drawing a flow sheet of an apparatus suitable for the purpose.

- The ore as it is received from the mine is crushed. and passed over a screen PIQt.

If, however, the ore 1s exposed to erably of about one fourth to three eighths inch mesh to separate the fines from the oversize.

The oversize is then delivered mto a slowly revolving brick lined kiln set at a suitable inclination and of such dimensons that the feed progresses through it at a s eed to deliver the ore at the dischar e en at adull red heat, this heat being su cient to -render the ore amenable to magnetic influence but not sufficient to roast 1t or cause any apparent chem1cal change in its constituents.

The fines, separated from the overslze, by-pass the kiln and combine with the heated ore when delivered from the discharge end of the kiln, and take up part of the heat from the oversize suflicient for the purposes of the process.

The whole product then passes through a revolving coolin mensions and instal atlon that the feed of heated ore progresses through it under such conditions of heat exchange and limitations of timefis' to deliver the ore at the discharge end at a temperature which will result 1n the maximum magnetic susceptibility being attained when the ore is properly cooled.

The cooling may take place in either a reducing atmosphere, a neutral atmosphere, or even a slightly oxidizing atmosphere, provided the ore is heated in lumps and the cooling operation is sufliclently slow to retain the magnetic susceptibillty of the ore.

To provide this atmosphere air may be blown through the cylinder counter current to the heated ore.-

From the cooling cylinder, the ore goes direct to the ball mill, where it is ground sulficientl fine to separate the different mineral particles, and from the ball mill the ground ore then passes to the electro-magnetic machines where the minerals are so arated.

' n a series of tests conducted to determine the value of this process for the separation of iron sulfid ores, it was ascertained that before heating only about 25% of the iron content was susceptible of magnetic attraction.

After heating the ore to the temperature above specified and immediately cooling it, 46.6% of the total iron content was separated.

After heating and allowing the ore, five c linder of such di-.

minutes to cool, 47.6% of the total iron content was separated."

After heating and allowing the ore ten minutes to cool, 66.8% of the total iron content Was separated.

After heating and allowing the ore fifteen minutes to cool, 76.2% of the total iron content was separated.

After heating and allowing the ore twenty minutes to cool, 77.9% of the total iron content was separated.

After heating and allowing the ore to be cooled for twelve minutes by an air blast and then immersed or quenched, 80.5% of the total iron content was separated, this separation representing practically the whole of the pyrrhotite.

What we claim is:

1. A process for the magnetic separation of ores which consists of heating the ore without roasting to a temperature ranging from 800 F. to 1200 F. which when the ore is properly cooled will yield the maximum susceptibility, then artificially cooling the ore under such conditions of heat exchange and time limitations ranging from five to fifteen minutes as to retain this susceptibility.

2. A process for the'magnetic separation of ores which consists of crushing the ore, separating the fines from the oversize, heating the latter to a temperature which will render the ore amenable to magnetic influence when properly cooled, combining the fines with the oversize when heated, and cooling the ore under such conditions as to retain its magnetic susceptibility.

3. A process for the magnetic separation of ores which consists of heating the ore ,without roasting to a temperature ranging CLARENCE THOM. RALPH WILLIAM DIAMOND. SELWXN GWILLYM BLAYLOCK.

Signed, sealed and delivered in the presence of- ANNIE ,MACKAY, CHAS. H. Rronns. 

